Dzhokhar Tsarnaev, poses for a photo after graduating from Cambridge Rindge and Latin High School. He has been charged with using a weapon of mass destruction. / Robin Young via AP

by Kevin Johnson, Donna Leinwand Leger and Aamer Madhani, USA TODAY

by Kevin Johnson, Donna Leinwand Leger and Aamer Madhani, USA TODAY

The heart of the criminal case against the surviving suspect in the Boston Marathon bombings is based on dramatic video and photographic evidence that prosecutors alleged Monday shows Dzhokhar Tsarnaev plainly placing a backpack believed to contain a powerful bomb at the exact site of the second explosion before calmly walking away.

A chilling frame-by-frame account, outlined in an 11-page criminal complaint unsealed Monday, offers the fullest description yet of the moments before two coordinated explosions rocked the iconic footrace, leaving three dead and more than 170 others injured.

The photographs and video, much of it captured on area surveillance cameras, allegedly show both Dzhokhar and brother Tamerlan Tsaranev in the final stages of the attack.

But with Tamerlan Tsarnaev, 26, now dead - killed in a confrontation with police early Friday morning - Dzhokhar Tsarnaev, 19, now stands alone to face criminal charges that carry a possible death sentence.

Lying in a Boston hospital, where he is listed in serious condition with a gunshot wound to the neck, Tsarnaev was formally charged Monday with one count of using and conspiring to use a weapon of mass destruction resulting in death and one count of using an explosive device in the malicious destruction of property, also resulting in death.

U.S. Magistrate Marianne Bowler, convening a brief hearing at the suspect's bedside, advised Tsarnaev of his rights and the charges against him.

"The court is satisfied that the defendant is alert and able to respond to charges,'' the court clerk noted in a record of the proceeding.

Assistant Federal Public Defender William Fick, who is representing Tsarnaev, did not respond to requests for comment.

That proceeding also marked an end to the government's use of a public safety exception to question the suspect about a possible continuing threat prior to informing him of his rights to legal counsel. Though the suspect's communication ability was limited because of a serious neck wound, he had been responding to questions in writing from investigators, a federal law enforcement official said.

The value of that information was not immediately clear, though the official, who is not authorized to comment publicly and spoke on condition of anonymity, said there is "growing confidence'' that no other threats exist.

"Although our investigation is ongoing, today's charges bring a successful end to a tragic week for the city of Boston and for our country,'' Attorney General Eric Holder said. "We've shown once again that those who target innocent Americans and attempt to terrorize our cities will not escape from justice.''

Boston Police Commissioner Ed Davis described the process of identifying and later finding the alleged "perpetrators of this savage act of terrorism'' just four days after the attack as a "herculean effort.''

And more of the same video and photographs credited with flushing the suspects from hiding after the FBI released selected images Thursday are expected to play an even larger role in Tsarnaev's prosecution, according to court documents made public Monday.

The first images of the suspects near the sites of the bombings are allegedly captured about 11 minutes before the first explosion, as the two men, carrying "large knapsacks'' are shown turning onto to Boylston Street, where the explosives were detonated, the court documents state.

While one stream of video allegedly follows Tamerlan Tsarnaev in the general direction of the first bomb site, a more detailed stream allegedly tracks Dzhokhar Tsarnaev to the second site just outside the Forum Restaurant, then packed with race-day spectators.

Shortly after 2:45 p.m., according to the documents, the video allegedly shows Tsarnaev, wearing a white baseball cap turned backward, "slipping his knapsack onto the ground'' as he stood among spectators along a metal barrier separating the crowd from the race course. A separate still photograph taken from the opposite side the street allegedly "shows the knapsack on the ground at (Tsarnaev's) feet.''

Seconds before the first explosion, video allegedly shows Tsarnaev appearing to speak into his cellphone. When the call is done, "a large crowd of people around him can be seen reacting to the first explosion,'' the documents state.

While "virtually every head turnsā?¦ and stares in apparent bewilderment and alarm,'' Tsarnarev "appears calm.''

The video then allegedly follows Tsarnaev walking "rapidly" away from the direction of the finish line, having left the pack at the location where he had been standing.

"Approximately 10 seconds later, an explosion occurs in the location where (Tsarnaev) had placed his knapsack,'' according to the documents.

The collection of video and photographs, while potentially damning, does not represent all of the government's case.

The documents also contain a dramatic witness account from the victim of a late Thursday night carjacking in Cambridge, Mass. The victim, who was not identified in court records, alleged that one the Tsarnaev brothers - believed to be Tamerlan Tsarnaev - approached the man's car and "tapped on the passenger-side window.'' When the window was rolled down, the suspect opened the door and allegedly pointed a firearm at the driver.

"Did you hear about the Boston explosion?'' the suspect told the driver. "I did that.'' The suspect then allegedly removed the ammunition clip from his gun to display a bullet before reinserting it, saying: "I am serious.''

The gunman forced the owner to drive to a second location where the second suspect was picked up and took a seat in the back. The gunman allegedly then took the wheel, moving the owner to the front passenger side of the car. And while they were driving, the gunman demanded money, receiving $45. One of the suspects, according to owner, also demanded the victim to surrender his ATM card and password.

When they stopped at a gas station and the two men left the vehicle, the "victim managed to escape.''

The incident immediately preceded the bloody confrontation with police where Tamerlan Tsarnaev was killed. His brother, who is accused of later abandoning the stolen car, was captured late Friday night, hiding in a boat parked in the driveway of a Watertown, Mass., residence.

Monday's legal action marks the beginning of a prosecution that will play out in civilian court despite some demands from Republican lawmakers that the suspect be treated as an enemy combatant and turned over to the military justice system.

"He will not be treated as an enemy combatant,'' White House Press Secretary Jay Carney said. "We will prosecute this terrorist through a civilian system of justice. Under U.S. law, United States citizens cannot be tried in military commissions.''

Vice President Biden, meanwhile, is scheduled to travel to Massachusetts on Wednesday to attend a memorial service for slain MIT police officer Sean Collier, according to a White House official source.

Collier was allegedly gunned down Thursday by the Tsarnaev brothers while the two were being sought by authorities. Charges related to Collier's killing were not included in the charges outlined Monday, but Holder said the investigation was continuing.

"We grieve with his family, his many friends and his fellow MIT Police officers," MIT President L. Rafael Reif said in a statement. "Many at MIT knew and loved Officer Sean Collier; for those who didn't, he was someone we could all wish to have had the opportunity to know."